Transmission device, reception device, communication system, transmission method, reception method, control circuit, and storage medium

Abstract

A transmission device (1) comprises: a plurality of transmission antennas (13a, 13b); a modulation unit (10) that generates a modulation signal; a coding rule selection unit (11) that selects a time-space block coding rule in correspondence to the value of the modulation signal (11); and a STBC coding unit (12), which is a coding unit that performs space-time block coding on the modulation signal using the selected time-space coding rule, thereby generating transmission signals respectively transmitted from the plurality of transmission antennas (13a, 13b).

Description

Transmitting device, receiving device, communication system, transmitting method, receiving method, control circuit, and storage medium

[0001] The present disclosure relates to a transmitting device, a receiving device, a communication system, a transmitting method, a receiving method, a control circuit, and a storage medium that perform transmit diversity transmission.

[0002] As modulation methods that have small envelope fluctuations and can achieve excellent power efficiency, the frequency shift keying (FSK) method and the phase shift keying (PSK) method are known.

[0003] Furthermore, as a method for improving transmission quality, transmit diversity methods have been proposed for wireless communication systems equipped with multiple transmit antennas, such as MISO (Multiple Input and Single Output) systems and MIMO (Multiple Input and Multiple Output) systems.

[0004] As one transmit diversity method, Non-Patent Document 1 discloses STBC (Space-Time Block Code) technology, which is a space-time block code. STBC technology generates multiple orthogonal sequences by performing complex conjugation and code inversion on multiple temporally consecutive symbols, and transmits each of the orthogonal sequences from a different transmit antenna. In STBC technology, the transmit sequence is orthogonally encoded in two dimensions, time and space. The encoding used in STBC technology, i.e., STBC encoding, is generally called Alamouti encoding. A receiver receiving an STBC-encoded transmit signal can easily estimate the transmit bit sequence by decoding the two received symbols using transmission path information. As a result, STBC technology can achieve a diversity gain equal to the number of transmit antennas, i.e., a transmit full diversity gain.

[0005] S. M. Alamouti, “A Simple Transmit Diversity Technique for Wireless Communications,” IEEE Journal on Select Areas in Communications, Vol. 16, No. 8, pp. 1451-1458, October 1998.

[0006] However, in the STBC technology, a code inversion process is performed between two consecutive symbols in a signal transmitted from one transmitting antenna. Therefore, when STBC coding is applied to a signal modulated by an FSK modulation method in which one symbol is composed of multiple samples, there is a problem in that the amplitude value periodically drops to 0 at symbol boundaries, increasing the amount of envelope fluctuation.

[0007] The present disclosure has been made in view of the above, and aims to provide a transmitting device that can suppress the amount of envelope fluctuation even when STBC coding is applied.

[0008] In order to solve the above-mentioned problems and achieve the objectives, the transmitting device according to the present disclosure is characterized by comprising a plurality of transmitting antennas, a modulation unit that generates modulated signals, a coding rule selection unit that selects a space-time block coding rule according to the value of the modulated signals, and a coding unit that generates transmission signals to be transmitted from each of the plurality of transmitting antennas by performing space-time block coding on the modulated signals using the selected space-time block coding rule.

[0009] The transmitting device according to the present disclosure has the effect of being able to suppress the amount of envelope fluctuation even when STBC coding is applied.

[0010] 1 is a diagram showing an example of the configuration of a communication system according to a first embodiment; FIG. 2 is a flowchart for explaining an example of a processing procedure of a transmitting device according to a first embodiment; FIG. 3 is a diagram showing an FSK signal in the frequency domain; FIG. 4 is a diagram showing a 4-value FSK signal in the frequency domain; FIG. 4 explains the encoding procedure of an STBC encoding unit; FIG. 5 is an explanatory diagram of a specific example of the encoding procedure of an STBC encoding unit for a 4-value FSK signal; FIG. 5 is a diagram showing an example of the configuration of a control circuit for realizing the functions of a communication system according to a first embodiment; FIG. 6 is a diagram showing an example of the configuration of a modulation unit according to a second embodiment;

[0011] A transmitting device, a receiving device, a communication system, a transmitting method, a receiving method, a control circuit, and a storage medium according to embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0012] 1 is a diagram showing an example of the configuration of a communication system 3 according to a first embodiment. The communication system 3 includes a transmitting device 1 and a receiving device 2.

[0013] The transmitting device 1 includes a modulation unit 10, a coding rule selection unit 11, an STBC encoding unit 12, and a plurality of transmitting antennas 13 a and 13 b. Hereinafter, when there is no need to distinguish between the transmitting antennas 13 a and 13 b, they may be simply referred to as transmitting antennas 13.

[0014] The modulator 10 generates a modulated signal by frequency shift keying. Specifically, the modulator 10 primarily modulates the input transmission bit sequence using the FSK method. That is, the modulator 10 maps the transmission bit sequence to an FSK-modulated symbol sequence. The transmission bit sequence may be a bit sequence that has been subjected to preprocessing such as interleaving and error correction coding. Hereinafter, a modulated signal that has been primarily modulated using the FSK method will also be referred to as an FSK signal.

[0015] The coding rule selection unit 11 selects an STBC coding rule to be used in the STBC encoding unit 12, depending on the value of the signal that has been primarily modulated by the modulation unit 10. A detailed method for selecting an STBC coding rule by the coding rule selection unit 11 will be described later, but the coding rule selection unit 11 selects one of two STBC coding rules that differ in the position of the negative sign, depending on the carrier frequency of the FSK signal.

[0016] The STBC coding unit 12 is an example of a coding unit that performs space-time block coding on the signal that has been primarily modulated by the modulation unit 10 using the STBC coding rule selected by the coding rule selection unit 11, thereby generating transmission signals to be transmitted from each of the multiple transmission antennas 13a, 13b, and outputs each of the generated transmission signals to the corresponding transmission antennas 13a, 13b.

[0017] The transmitting antennas 13a and 13b radiate the transmission signal output from the STBC encoding unit 12 as radio waves.

[0018] Furthermore, the transmitting device 1 may add a cyclic prefix (CP) to the STBC encoding result or perform post-processing such as spreading. When adding a CP, for example, CP adding units are provided between the STBC encoding unit 12 and each of the transmitting antennas 13 a and 13 b, the number of which corresponds to the number of transmitting antennas 13, and the STBC encoding unit 12 outputs the processed signal to the corresponding CP adding unit. The CP adding unit adds a CP to the signal output from the STBC encoding unit 12 and outputs the CP-added signal to the corresponding transmitting antenna 13. When spreading is performed, for example, spreading processing units are provided between the STBC encoding unit 12 and each of the transmitting antennas 13 a and 13 b, the number of which corresponds to the number of transmitting antennas 13. The STBC encoding unit 12 outputs the processed signal to the corresponding spreading processing unit. The spreading processing unit multiplies the signal output from the STBC encoding unit 12 by a spreading sequence and outputs the spread signal to the corresponding transmitting antenna 13.

[0019] Here, an example is described in which the transmitting device 1 has two transmitting antennas 13, but the transmitting device 1 may have three or more transmitting antennas 13. That is, the transmitting device 1 only needs to have two or more transmitting antennas 13. When there are three or more transmitting antennas 13, the STBC encoding unit 12 generates transmission signals for the number of transmitting antennas 13 and outputs each of the generated transmission signals to the corresponding transmitting antenna 13.

[0020] 1 illustrates components of the transmitting device 1 that are involved in baseband signal processing, the transmitting device 1 may also include components that are not illustrated in Fig. 1. For example, the transmitting device 1 may also include a filter, an analog section that performs analog signal processing, and the like, in addition to the components illustrated in Fig. 1.

[0021] This embodiment is based on the premise that Alamouti coding is used as the transmission diversity method, i.e., STBC coding. Furthermore, in this embodiment, the STBC coding unit is called a "block," and the unit of frequency shift keying, i.e., the data unit of FSK modulation, is called a "symbol." An FSK-modulated signal is a signal with a frequency corresponding to the bit value, and is a signal sampled at a certain time interval. A "symbol," which is an FSK-modulated signal, is a signal with a frequency corresponding to the bit value, and the time signals constituting a "symbol" are called "samples."

[0022] In this embodiment, the description is based on the premise that FSK modulation is performed as the primary modulation, but the primary modulation method is not limited to FSK modulation and may be a modulation method that transmits information based on the amount of phase rotation between signal points, such as MSK (Minimum Shift Keying) modulation or GMSK (Gaussian MSK) modulation. The primary modulation method is preferably a modulation method having constant envelope.

[0023] The receiving device 2 includes a receiving antenna 20, a coding rule selecting unit 21, an STBC decoding unit 22, and a demodulating unit 23.

[0024] The receiving antenna 20 receives the signal transmitted from the transmitting device 1 as a received signal, and outputs the received signal to the coding rule selecting unit 21 and the STBC decoding unit 22, respectively.

[0025] The coding rule selection unit 21 selects the same coding rule as the STBC coding rule used in the transmitting device 1, and outputs the selected STBC coding rule to the STBC decoding unit 22. Note that the transmitting device 1 may notify the receiving device 2 of the STBC coding rule used on the transmitting side by using a pilot signal or the like included in the transmitted signal, or the receiving device 2 may estimate the STBC coding rule used on the transmitting side based on the received signal. The coding rule selection unit 21 may select the STBC coding rule used in the transmitting device 1 by any method.

[0026] The STBC decoder 22 performs STBC decoding on the received signal using the STBC coding rule selected by the coding rule selector 21 , and outputs the decoded signal to the demodulator 23 .

[0027] The demodulation unit 23 performs demodulation, i.e., frequency shift demodulation, corresponding to the FSK method, which is the primary modulation, on the decoded signal that is the result of decoding by the STBC decoding unit 22, to obtain an estimated bit sequence that is an estimation result of the transmitted bit sequence.

[0028] If the transmitting device 1 has performed preprocessing such as error correction coding on the transmission bit sequence, the receiving device 2 performs decoding processing corresponding to the preprocessing, such as deinterleaving and error correction decoding, on the demodulation result by the demodulation unit 23. If soft-decision error correction decoding is performed on the demodulation result by the demodulation unit 23, the demodulation unit 23 may determine a soft-decision value. If the transmitting device 1 has added a CP, the receiving device 2 includes a CP removal unit that removes the CP subsequent to the receiving antenna 20, and the received signal from which the CP has been removed by the CP removal unit is output to the coding rule selection unit 21 and the STBC decoding unit 22, respectively.

[0029] 1 shows an example in which there is one receiving antenna 20, there may be multiple receiving antennas 20. When there are multiple receiving antennas 20, the coding rule selection unit 21 or a receiving diversity decoding unit (not shown) provided before the coding rule selection unit 21 combines multiple received signals received by the multiple receiving antennas 20, and the STBC decoding unit 22 performs STBC decoding on the combined received signal.

[0030] Note that, although FIG. 1 illustrates components of the receiving device 2 related to baseband signal processing, the receiving device 2 may also include components not illustrated in FIG. 1. For example, the receiving device 2 also performs time synchronization processing, frequency synchronization processing, transmission channel estimation, etc., but since these processes can be performed using general processing, illustration and description of the functional units that perform these processes will be omitted. In the following description of the operation of the receiving device 2, it will be assumed that the time synchronization processing, frequency synchronization processing, transmission channel estimation processing, etc. are performed ideally. If the time synchronization processing, frequency synchronization processing, transmission channel estimation processing, etc. are not performed ideally, errors may occur. However, since the method of dealing with errors is the same as that of a receiving device that performs general STBC decoding, description thereof will be omitted here.

[0031] Next, an operation of the communication system 3 according to the first embodiment will be described. First, an overall operation of the transmitting device 1 will be described. Fig. 2 is a flowchart for explaining an example of a processing procedure of the transmitting device 1 according to the first embodiment.

[0032] The modulation unit 10 of the transmitting device 1 generates an FSK signal by FSK modulation of the input transmission bit sequence (step S101). The modulation unit 10 outputs the generated FSK signal to the coding rule selection unit 11 and the STBC encoding unit 12.

[0033] The coding rule selection unit 11 selects an STBC coding rule based on the FSK signal output from the modulation unit 10 (step S102). The coding rule selection unit 11 outputs the selected STBC coding rule to the STBC encoding unit 12.

[0034] The STBC encoder 12 generates an STBC-coded signal by performing STBC encoding on samples in the symbols of the FSK signal output by the modulator 10 using the STBC coding rule selected by the coding rule selector 11. The STBC encoder 12 generates a transmission signal by dividing the STBC-coded signal into signals corresponding to the transmitting antennas 13 a and 13 b (step S103). The STBC encoder 12 outputs each of the generated transmission signals to the corresponding transmitting antennas 13 a and 13 b.

[0035] An FSK signal has the advantage of having little envelope fluctuation, but when STBC coding is performed between symbols, the amplitude value periodically drops to 0 at the symbol boundaries due to the code inversion process performed on temporally consecutive symbols. This causes the envelope of the transmission signal to fluctuate. In this embodiment, in order to suppress the envelope fluctuation, STBC coding is performed within the symbols of the FSK signal based on the carrier frequency of the FSK signal so as to reduce the influence of the code inversion process on temporally consecutive symbols while maintaining the space-time orthogonality in the STBC coding. Details of the method for selecting the STBC coding rule and the STBC coding process within a symbol will be described later.

[0036] The transmitting antennas 13a and 13b transmit the transmission signal output from the STBC encoding unit 12 as radio waves to the receiving device 2 (step S104).

[0037] Next, the functions of the coding rule selector 11 and the STBC encoder 12 of the transmitter 1 will be described. The coding rule selector 11 selects one of a plurality of STBC coding rules with different positions of the negative sign based on the frequency carrier of the FSK signal output from the modulator 10. FIG. 3 is a diagram showing an FSK signal in the frequency domain. FIG. 3 shows an FSK signal in the frequency domain having M frequency carriers output from the modulator 10. As shown in FIG. 3, the coding rule selector 11 selects an STBC coding rule based on the value of the input FSK signal so that different STBC coding rules are applied to adjacent FSK carriers in the frequency domain for the M FSK carriers.

[0038] FIG. 4 is a diagram illustrating a four-level FSK signal in the frequency domain. The FSK signal shown in FIG. 4 has M=4, and is assigned a frequency carrier of f1 when the transmission bit sequence is "00," f2 when the transmission bit sequence is "01," -f2 when the transmission bit sequence is "10," and -f1 when the transmission bit sequence is "11." The modulation unit 10 generates an FSK signal by selecting a frequency corresponding to the transmission bit sequence. The coding rule selection unit 11 selects coding rule #1 when the frequency of the FSK signal is f1 or -f2, and selects coding rule #2 when the frequency of the FSK signal is f2 or -f1, so that different STBC coding rules are selected between adjacent FSK carriers.

[0039] Here, coding rule #1 is expressed by the following formula (1). In formula (1), x (k) t represents the t-th transmission signal in the STBC block transmitted from the k-th transmission antenna 13. t represents the t-th FSK signal among the FSK signals to be STBC encoded. k and t are natural numbers. The maximum value of t is determined according to the size of the STBC code, and in this embodiment, t=2. In the configuration example shown in FIG. 1, the transmitting antenna 13a is the first transmitting antenna 13, and the transmitting antenna 13b is the second transmitting antenna 13. * indicates a complex conjugate.

[0040]

[0041] Coding rule #2 is expressed by the following equation (2): Coding rule #2 differs from coding rule #1 in the position of the negative sign.

[0042]

[0043] 5 is an explanatory diagram of the encoding procedure of the STBC encoder 12. The STBC encoder 12 performs STBC encoding within the FSK symbols of the FSK signal output from the modulator 10 using the STBC encoding rule selected by the coding rule selector 11. The STBC encoder 12 performs STBC encoding using a combination of FSK samples separated by (M / 2-1) samples within the same FSK symbol, where the 0th to (M / 2-1)th FSK samples of one symbol of the FSK signal consisting of M samples are designated as z0 in Equation (1) and Equation (2), and the M / 2nd to (M-1)th FSK samples are designated as z1 in Equation (1) and Equation (2). Here, a combination of FSK samples separated by (M / 2-1) samples refers to a combination in which (M / 2-1) FSK samples are sandwiched between two FSK samples.

[0044] 6 is a diagram illustrating a specific example of the encoding procedure of the STBC encoder 12 for a 4-level FSK signal. In FIG. 6, the modulator 10 generates an FSK symbol consisting of four samples, where the 0th symbol has an FSK signal frequency of f1, i.e., an information bit sequence of "00", and the 1st symbol has an FSK signal frequency of f2, i.e., an information bit sequence of "01". In this case, the coding rule selector 11 selects coding rule #1 for the 0th symbol and coding rule #2 for the 1st symbol. The STBC encoder 12 first generates an STBC-encoded signal using coding rule #1 shown in Equation (1), with the FSK signal of the 0th sample of the 0th symbol and the FSK signal of the 2nd sample set to z0 and z1, respectively, and then encodes the 0th sample of the 0th symbol of the STBC-encoded signal using x. (k) 0, the second sample x (k) Similarly, the FSK signal of the first sample of the 0th symbol is set to z0, the FSK signal of the third sample is set to z1, and an STBC coded signal is generated using coding rule #1 shown in equation (1). The first sample of the 0th symbol of the STBC coded signal is set to x (k) 0, 3rd sample x (k) 1. The first symbol of the STBC coded signal is generated using coding rule #2 in the same way as the zeroth symbol.

[0045] FIG. 6 shows transmit signals TX1 and TX2 after STBC encoding. Transmit signal TX1 is a signal transmitted from transmit antenna 13a where k=1, and transmit signal TX2 is a signal transmitted from transmit antenna 13b where k=2. FIG. 6 also shows signal point transitions in transmit signal TX2. The numbers in brackets [ ] in the figure indicate the order of samples within each FSK symbol; for example, [0] indicates the 0th sample. As shown in FIG. 6, signal point transitions at transmit antenna 13b are continuous within and between FSK symbols, confirming that the increase in envelope fluctuation due to STBC encoding has been suppressed.

[0046] In this embodiment, the coding rule selector 11 selects an STBC coding rule in which the position of the negative sign differs between adjacent FSK carriers, thereby suppressing an increase in the amount of envelope fluctuation between FSK symbols, in accordance with the frequency of the FSK signal output from the modulator 10. Furthermore, the STBC encoder 12 performs STBC encoding using a combination of the 0th to (M / 2-1)th samples and the M / 2th to M-1th samples of the FSK symbol using the selected STBC coding rule, thereby suppressing an increase in the amount of envelope fluctuation within the FSK symbol.

[0047] 4, the coding rule selection unit 11 selects coding rule #1 expressed by equation (1) when the frequency of the FSK signal output from the modulation unit 10 is f1, i.e., the transmission bit sequence is "00," and when the frequency of the FSK signal is -f2, i.e., the transmission bit sequence is "10," and selects coding rule #2 expressed by equation (2) when the frequency of the FSK signal is f2, i.e., the transmission bit sequence is "01," and when the frequency of the FSK signal is -f1, i.e., the transmission bit sequence is "11." However, the coding rule assignment may be reversed. That is, the coding rule selection unit 11 may select coding rule #2 expressed by Equation (2) when the frequency of the FSK signal output from the modulation unit 10 is f1, i.e., the transmission bit sequence is "00," and when the frequency of the FSK signal is -f2, i.e., the transmission bit sequence is "10," and may select coding rule #1 expressed by Equation (1) when the frequency of the FSK signal is f2, i.e., the transmission bit sequence is "01," and when the frequency of the FSK signal is -f1, i.e., the transmission bit sequence is "11." Furthermore, the STBC coding rule selected by the coding rule selection unit 11 may be other than the STBC coding rules expressed by Equation (1) and Equation (2), and may select a combination of STBC coding rules such that the STBC-coded signal at each transmitting antenna 13 is phase continuous within and between symbols.

[0048] Furthermore, when the modulation unit 10 performs L-times oversampling on the FSK signal by phase interpolation, the STBC encoding unit 12 can perform STBC encoding using the FSK signals from 0 to (ML / 2-1) samples and from ML / 2 to ML-1 samples, thereby achieving the same effect.

[0049] As described above, the transmitting device 1 according to the first embodiment includes multiple transmitting antennas 13 a and 13 b, a modulator 10 that generates modulated signals, a coding rule selector 11 that selects a space-time block coding rule in accordance with the value of the modulated signals, and an STBC encoder 12 that is a coding unit that performs space-time block coding on the modulated signals using the selected space-time block coding rule to generate transmission signals to be transmitted from each of the multiple transmitting antennas 13 a and 13 b. The modulator 10 can generate an FSK signal as a modulated signal by performing modulation using an FSK system. The coding rule selector 11 can select an STBC coding rule based on the value of the frequency carrier of the modulated signal modulated using the FSK system. More specifically, the coding rule selector 11 selects the STBC coding rule based on the value of the modulated signal so that different STBC coding rules are applied to adjacent frequency carriers in the frequency domain of the frequency carrier of the modulated signal that has been primarily modulated using the FSK system. In this case, the coding rule selector 11 selects an STBC coding rule such that STBC coding rules with different negative sign positions are applied to adjacent frequency carriers in the frequency domain. Furthermore, the STBC encoder 12 performs STBC coding within an FSK symbol using the selected STBC coding rule, thereby suppressing an increase in the envelope fluctuation of a transmission signal compared to conventional STBC coding, even when STBC coding is applied to a signal primarily modulated by FSK. For example, the above configuration can achieve an envelope fluctuation equivalent to that of an FSK signal at one branch before STBC coding. Therefore, in this embodiment, a decrease in power efficiency can be prevented at each transmitting antenna 13 compared to conventional STBC coding. Furthermore, the processing in the STBC encoder 12 maintains time-space orthogonality between the transmitting antennas 13, as in conventional STBC coding, thereby preventing a decrease in transmit diversity gain.

[0050] In the first embodiment, it is assumed that Alamouti coding is used as the STBC coding. However, the STBC coding unit 12 may use an STBC coding method other than Alamouti coding. The coding method used by the STBC coding unit 12 may be any method that performs coding by complex conjugation and sign inversion of a signal.

[0051] Next, a description will be given of a hardware configuration for realizing the communication system 3. The functions of the modulation unit 10, the coding rule selection unit 11, the STBC encoding unit 12, the coding rule selection unit 21, the STBC decoding unit 22, and the demodulation unit 23 are realized by a processing circuit, which is an electronic circuit.

[0052] The processing circuit may be dedicated hardware, or may be a control circuit including a memory and a CPU (Central Processing Unit) that executes a program stored in the memory.

[0053] When the processing circuitry is implemented by dedicated hardware, the processing circuitry may be a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof.

[0054] When the processing circuit is a control circuit including a memory and a CPU that executes a program stored in the memory, the control circuit is, for example, a control circuit 300 shown in Fig. 7. Fig. 7 is a diagram showing an example of the configuration of the control circuit 300 for realizing the functions of the communication system 3 according to the first embodiment. The control circuit 300 includes a processor 300a and a memory 300b.

[0055] The processor 300a reads and executes programs corresponding to each process stored in the memory 300b, thereby realizing the functions of the communication system 3. The processor 300a is a CPU, and is also called an arithmetic unit, a microprocessor, a microcomputer, a DSP (Digital Signal Processor), etc.

[0056] The memory 300b is, for example, a non-volatile or volatile semiconductor memory such as a random access memory (RAM), a read only memory (ROM), a flash memory, an erasable programmable read only memory (EPROM), an electrically programmable programmable read only memory (EEPROM), a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, a digital versatile disk (DVD), etc. The memory 300b is also used as a temporary memory for each process executed by the processor 300a.

[0057] Note that the functions of the modulation unit 10, coding rule selection unit 11, and STBC encoding unit 12 of the transmission device 1 may be realized by different processing circuits, or the functions of the modulation unit 10, coding rule selection unit 11, and STBC encoding unit 12 may be realized together by a single processing circuit. The same applies to the coding rule selection unit 21, STBC decoding unit 22, and demodulation unit 23 of the reception device 2. Furthermore, the functions of the transmission device 1 and the reception device 2 may be realized by combining dedicated hardware and a CPU. Furthermore, the division of the functional units of the transmission device 1 and the reception device 2 is an example, and a component described as a single functional unit may be realized using multiple processing circuits.

[0058] Second Embodiment Fig. 8 is a diagram showing an example of the configuration of a modulation unit 10a according to a second embodiment. Note that a transmission device 1a (not shown) according to the second embodiment is similar to the transmission device 1 according to the first embodiment, except that it has a modulation unit 10a instead of the modulation unit 10. Below, differences from the first embodiment will be mainly described, and descriptions of the same parts as in the first embodiment will be omitted.

[0059] In the first embodiment, the modulation unit 10 shown in FIG. 1 uses a modulation method, such as FSK modulation, as primary modulation of a transmission bit sequence, which transmits information based on the amount of phase rotation between samples. In the second embodiment, the modulation unit 10a spreads the transmission bit sequence and modulates the spread bit sequence using a π / 4-shift Quadrature Amplitude Modulation (QAM) shift method, thereby achieving the same effect as in the first embodiment. In other words, in the second embodiment, spreading is performed on a modulation method that transmits information based on the phase of each sample point, thereby keeping the envelope fluctuation amount constant and achieving the same effect as in the first embodiment.

[0060] The modulation section 10 a includes a spreading bit generation section 100 and a shift QAM section 101 .

[0061] The spreading bit generator 100 generates a spreading bit sequence from the input transmission bit sequence. Specifically, the spreading bit generator 100 generates a spreading bit sequence consisting of N samples based on a specified spreading factor N and the modulation method used by the shift QAM unit 101. The spreading bit generator 100 outputs the generated spreading bit sequence to the shift QAM unit 101.

[0062] The shift QAM unit 101 primarily modulates the spread bit sequence for N samples output by the spread bit generation unit 100 using a shift QAM method corresponding to the spreading factor N, and generates a modulated signal including a mapped modulated symbol sequence. The shift QAM unit 101 outputs the generated modulated signal to each of the coding rule selection unit 11 and the STBC encoding unit 12.

[0063] Here, an example will be described in which the spreading factor N of the spreading bit generation unit 100 is 4 and the modulation method used by the shift QAM unit 101 is π / 4 shift QPSK. However, the modulation unit 10a is not limited to this example, and the spreading factor N may be other than 4, and the modulation method used by the shift QAM unit 101 may be a modulation method other than π / 4 shift QPSK. For example, the modulation unit 10a may set the spreading factor N of the spreading bit generation unit 100 to 4 and the modulation method used by the shift QAM unit 101 to π / 4 shift DQPSK (Differential QPSK). Alternatively, the modulation unit 10a may set the spreading factor N of the spreading bit generation unit 100 to 2 and the modulation method used by the shift QAM unit 101 to π / 2 shift BPSK (Binary Phase Shift Keying).

[0064] 9 is an explanatory diagram of the operation of the spread bit generator 100 of the modulator 10a shown in FIG. 8 . FIG. 9 shows an example in which the spreading factor N of the spread bit generator 100 is 4 and the modulation method used by the shift QAM unit 101 is π / 4 shift QPSK. For even-numbered symbols, when the transmission bit sequence is “00,” the spread bit generator 100 generates a spread bit sequence of four samples, “00,” “00,” “01,” and “01,” and outputs the sequence to the shift QAM unit 101. Similarly, when the transmission bit sequence is “01,” the spread bit generator 100 generates a spread bit sequence of four samples, “00,” “01,” “10,” and “00,” when the transmission bit sequence is “10,” the spread bit generator 100 generates a spread bit sequence of four samples, “00,” “11,” “01,” and “10,” when the transmission bit sequence is “11,” and the spread bit sequence of four samples, “00,” “10,” “10,” and “11,” when the transmission bit sequence is “11.” Furthermore, for odd-numbered symbols, when the transmission bit sequence is "00", the spreading bit generator 100 generates a spreading bit sequence of four samples of "11", "11", "10", and "10", and outputs these to the shift QAM unit 101. Similarly, when the transmission bit sequence is "01", the spreading bit generator 100 generates a spreading bit sequence of four samples of "11", "10", "01", and "11", when the transmission bit sequence is "10", the spreading bit generator 100 generates a spreading bit sequence of four samples of "11", "00", "10", and "01", when the transmission bit sequence is "11", and generates a spreading bit sequence of four samples of "11", "01", "01", and "00", when the transmission bit sequence is "11".

[0065] 10 is an explanatory diagram of the operation of the shift QAM unit 101 of the modulation unit 10a shown in FIG. 8. The shift QAM unit 101 generates a modulated signal by mapping the four-sample spread bit sequence output by the spread bit generation unit 100 using a π / 4 shift QPSK scheme in which the mapping point shifts by π / 4 for each sample. Here, for even-numbered samples, the shift QAM unit 101 maps each sample to a phase of "0" if the spread bit sequence value is "00," a phase of "π / 2" if the spread bit sequence value is "01," a phase of "-π / 2" if the spread bit sequence value is "10," and a phase of "π" if the spread bit sequence value is "11." Furthermore, here, for odd-numbered samples, the shift QAM unit 101 maps each sample to a phase of "π / 4" when the value of the spreading bit sequence is "00", to a phase of "3π / 4" when the value of the spreading bit sequence is "01", to a phase of "-π / 4" when the value of the spreading bit sequence is "10", and to a phase of "-3π / 4" when the value of the spreading bit sequence is "11".

[0066] The coding rule selector 11 of the transmitter 1a selects a coding rule based on the value of the N / 2-th sample of the N samples from 0 to N-1 of the modulated signal output from the modulator 10a. For example, in the case of N=4 shown in Figures 9 and 10, the coding rule selector 11 selects a coding rule based on the value of the second sample of the four samples from 0 to 3. Specifically, when the N / 2-th sample of the modulated signal is a signal point corresponding to a phase of π / 2, the coding rule selector 11 selects coding rule #1 expressed by the above formula (1), and when the N / 2-th sample of the modulated signal is a signal point corresponding to a phase of -π / 2, the coding rule selector 11 selects coding rule #2 expressed by the above formula (2).

[0067] In the example shown in Figure 10, the shift QAM unit 101 maps signal points on the I / Q axis for even samples, but may also map signal points on the I / Q axis for odd samples.In this case, the coding rule selection unit 11 may select coding rule #1 expressed by the above formula (1) when the N / 2-th sample of the modulated signal is a signal point corresponding to a phase of 3π / 4, and may select coding rule #2 expressed by the above formula (2) when the N / 2-th sample of the modulated signal is a signal point corresponding to a phase of -3π / 4.In addition, the correspondence between the coding rule and the modulated signal value may be reversed. In other words, in the above, coding rule selection unit 11 selects coding rule #1 when the N / 2-th sample of the modulated signal is a signal point corresponding to a phase of π / 2, and coding rule #2 when the N / 2-th sample of the modulated signal is a signal point corresponding to a phase of -π / 2, but it may also be configured to select coding rule #1 when the N / 2-th sample of the modulated signal is a signal point corresponding to a phase of -π / 2, and coding rule #2 when the N / 2-th sample of the modulated signal is a signal point corresponding to a phase of π / 2.

[0068] The STBC encoder 12 of the transmitting device 1a performs STBC encoding on the modulated signal output from the modulator 10a using the STBC coding rule selected by the coding rule selector 11. Note that the STBC encoding operation in the STBC encoder 12 is the same as in the first embodiment, and performs STBC encoding using a combination of the 0th to (N / 2-1)th samples and the N / 2th to (N-1)th samples of the modulation symbol made up of N samples.

[0069] As described above, the transmitting device 1a according to the second embodiment generates a spread bit sequence, performs shift QAM modulation on the generated spread bit sequence, and selects an STBC coding rule according to the value of the shift QAM modulated symbol, thereby achieving the same effects as those of the first embodiment. The configuration and operation of the receiving side in the second embodiment are the same as those of the receiving device 2 according to the first embodiment, and therefore will not be described here.

[0070] As described above, the modulation unit 10a of the transmission device 1a according to the second embodiment includes a spreading bit generation unit 100 that generates a spreading bit sequence from an input transmission bit sequence, and a shift QAM unit 101 that generates a modulated signal from the spreading bit sequence using a shift QAM modulation method. For a spreading factor of N, the modulated signal is composed of n samples, from 0th to N-1th. In this case, the coding rule selection unit 11 selects an STBC coding rule based on the value of the N / 2th sample of the modulated signal. The spreading bit generation unit 100 generates a spreading bit sequence from the transmission bit sequence based on the modulation method used by the shift QAM unit 101 and a predetermined spreading factor N. The transmission device 1a having such a modulation unit 10a can also suppress an increase in the amount of envelope fluctuation of the transmission signal, similar to the transmission device 1 according to the first embodiment.

[0071] The hardware configuration of the transmitting device 1a is also the same as that of the transmitting device 1 according to the first embodiment, and therefore a description thereof will be omitted here.

[0072] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0073] For example, coding rules #1 and #2 shown above in equations (1) and (2) are also examples, and if the position of the negative sign is different between coding rules #1 and #2, they are not limited to those expressed in equations (1) and (2).

[0074] 1, 1a transmitter, 2 receiver, 3 communication system, 10, 10a modulator, 11, 21 coding rule selector, 12 STBC encoder, 13, 13a, 13b transmitter antenna, 20 receiver antenna, 22 STBC decoder, 23 demodulator, 100 spread bit generator, 101 shift QAM unit, 300 control circuit, 300a processor, 300b memory.

Claims

1. A plurality of transmitting antennas; A modulation unit that generates a modulated signal; A coding rule selection unit that selects a space-time block coding rule in response to a value of the modulated signal; a coding unit that performs space-time block coding on the modulated signal using the selected space-time block coding rule to generate a transmission signal to be transmitted from each of the plurality of transmitting antennas; A transmitting device comprising:

2. The modulation unit is 2. The transmitting device according to claim 1, wherein the modulated signal is generated by frequency shift keying.

3. The coding rule selection unit 3. The transmitting apparatus according to claim 2, wherein the space-time block coding rule is selected based on a value of a frequency carrier of the modulated signal modulated by the frequency shift keying.

4. The coding rule selection unit The transmitting device according to claim 3, characterized in that the space-time block coding rule is selected based on a value of the modulated signal so that different space-time block coding rules are applied to adjacent frequency carriers in the frequency domain in the frequency carriers of the modulated signal modulated by the frequency shift keying.

5. The transmitting device according to claim 4, characterized in that the coding rule selection unit selects the space-time block coding rule such that the space-time block coding rule in which the positions of the negative signs are different are applied to the frequency carriers adjacent to each other in the frequency domain.

6. The modulation unit is a spreading bit generator for generating a spreading bit sequence from an input transmission bit sequence; a shift quadrature amplitude modulation unit that generates the modulated signal from the spread bit sequence by a shift quadrature amplitude modulation method; 2. The transmitting device according to claim 1, further comprising:

7. The modulated signal is composed of n samples from 0th to n-1th samples, The transmitting device according to claim 6 , wherein the coding rule selection unit selects the space-time block coding rule based on a value of an n / 2-th sample of the modulated signal.

8. The transmitting device according to claim 6 or 7, characterized in that the spread bit generation unit generates the spread bit sequence from the transmission bit sequence based on a modulation scheme used by the shift quadrature amplitude modulation unit and a predetermined spreading factor.

9. The modulated signal is composed of n samples from 0th to n-1th samples, The transmitting device according to any one of claims 3 to 7, characterized in that the encoding unit performs the space-time block encoding using a combination of samples arranged with n / 2-1 samples between them within the same symbol of the modulated signal.

10. A receiving device that receives a transmission signal transmitted by the transmitting device according to claim 1 as a received signal, comprising: a coding rule selection unit that selects the space-time block coding rule used in the transmitting device for the received signal; a decoding unit that performs space-time block decoding on the received signal using the selected space-time block coding rule; a demodulation unit that demodulates a result of the decoding by the decoding unit; A receiving device comprising:

11. A transmitting device according to claim 1 ; A receiving device according to claim 10; A communication system comprising:

12. A transmitting device having a plurality of transmitting antennas, a modulating step for generating a modulated signal; a coding rule selection step of selecting a space-time block coding rule in response to a value of the modulated signal; an encoding step of performing space-time block coding on the modulated signal using the selected space-time block coding rule to generate a transmission signal to be transmitted from each of the plurality of transmitting antennas; A transmission method comprising:

13. In the modulating step, The transmission method according to claim 12, wherein the transmitting device generates the modulated signal by frequency shift keying.

14. In the code rule selection step, The transmission method according to claim 13, characterized in that the transmitting device selects the space-time block coding rule based on a value of a frequency carrier of the modulated signal modulated by the frequency shift keying.

15. In the code rule selection step, The transmission method according to claim 14, characterized in that the transmitting device selects the space-time block coding rule based on a value of the modulated signal such that different space-time block coding rules are applied to adjacent frequency carriers in the frequency domain in the frequency carriers of the modulated signal modulated by the frequency shift keying.

16. In the code rule selection step, The transmission method according to claim 15, characterized in that the transmission device selects the space-time block coding rule such that the positions of the negative signs are different between the frequency carriers adjacent in the frequency domain.

17. The modulating step includes: a spreading step of generating a spread bit sequence from an input transmission bit sequence; a shift quadrature amplitude modulation step of generating the modulated signal from the spread bit sequence by a shift quadrature amplitude modulation method; The method of claim 12, further comprising:

18. The modulated signal is composed of n samples from 0th to n-1th samples, In the code rule selection step, The transmission method according to claim 17, characterized in that the transmitting device selects the space-time block coding rule based on a value of the n / 2-th sample of the modulated signal.

19. In the diffusion step, The transmission method according to claim 17 or 18, characterized in that the transmission device generates the spread bit sequence from the transmission bit sequence based on a modulation scheme used in the shift quadrature amplitude modulation step and a predetermined spreading factor.

20. The modulated signal is composed of n samples from 0th to n-1th samples, A transmission method according to any one of claims 14 to 18, characterized in that in the encoding step, the transmitting device performs the space-time block encoding using a combination of samples arranged with n / 2-1 samples between them within the same symbol of the modulated signal.

21. A receiving device that receives a transmission signal transmitted by the transmission method according to claim 12 as a received signal, a coding rule selection step of selecting, for the received signal, the space-time block coding rule used in the transmission method; a decoding step of performing space-time block decoding on the received signal using the selected space-time block coding rule; a demodulation step of demodulating a result of the decoding step; A receiving method comprising:

22. A control circuit for controlling a transmitting device having a plurality of transmitting antennas, a modulating step for generating a modulated signal; a coding rule selection step of selecting a space-time block coding rule in response to a value of the modulated signal; an encoding step of performing space-time block coding on the modulated signal using the selected space-time block coding rule to generate a transmission signal to be transmitted from each of the plurality of transmitting antennas; A control circuit that causes the transmitting device to execute the above.

23. In a storage medium storing a program for controlling a transmitting device having a plurality of transmitting antennas, the program a modulating step for generating a modulated signal; a coding rule selection step of selecting a space-time block coding rule in response to a value of the modulated signal; an encoding step of performing space-time block coding on the modulated signal using the selected space-time block coding rule to generate a transmission signal to be transmitted from each of the plurality of transmitting antennas; A storage medium that causes the transmitting device to execute the above.